This study is to evaluate the safety and toxicity of sodium phenylbutyrate (PB) given as a intravenous continuous infusion for seven days to patients with DBS and relapsed AML, to estimate the pharmacokinetics of PB in this patient population, to escalate the doses to achieve a targeted plasma level of 5mM is tolerable and to obtain preliminary clinical and/or laboratory-based data suggesting potential therapeutic activity of this drug for patients with myeloid malignancies.